Document Type



Doctor of Philosophy (PhD)



First Advisor's Name

Dr. Timothy M. Collins

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Dr. Alessandro Catenazzi

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Dr. Joel T. Heinen

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Dr. Kenneth L. Krysko

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Dr. Sparkle L. Malone

Fifth Advisor's Committee Title

Committee member


genetics, invasion biology, herpetology, geckos, reptiles, squamates, non-native species

Date of Defense



Biological invasions cause tremendous damage to ecosystems, economies, and human livelihoods worldwide. Florida is home to more established non-native species of reptiles and amphibians than anywhere else on Earth, many of which cause substantial harm to native biodiversity and human well-being. The relatively new discipline of invasion genetics promises to significantly improve the understanding, prediction, prevention, and management of biological invasions. The purpose of this dissertation is to utilize invasion genetics techniques to further understanding of the patterns and processes of biological invasions, especially as they pertain to Florida’s destructive and diverse non-native squamate reptile assemblage. In the first phase of my dissertation, I sequence mitochondrial DNA (mtDNA) from non-native Phelsuma and Gekko populations in southern Florida, and compare these sequences to georeferenced native-range sequence data. I positively identify these non-native gekkonids as Phelsuma grandis Gray 1870 and Gekko gecko (Linnaeus 1758), and establish that southern Florida populations of both species derive from multiple, divergent native-range source populations, thereby highlighting the potential for elevated population-level genetic diversity due to admixture between genetically distinct source populations. In the case of G. gecko, extremely high pairwise sequence divergences suggest the introduction of multiple subspecies to southern Florida, a hypothesis that I test and confirm in the next phase of my dissertation using a combination of mtDNA, nuclear DNA (nDNA), and morphological data. One of these subspecies is apparently undescribed, and potentially threatened in its native range by indiscriminate harvesting for the Traditional Asian Medicine trade, illustrating how invasion genetics studies can also be useful for addressing fundamental taxonomic questions. Finally, I build upon my aforementioned positive genetic identification of P. grandis by constructing bioclimatic Species Distribution Models (SDMs) using Florida and native-range P. grandis occurrence data. I show that these SDMs would not have predicted the successful colonization Florida by P. grandis, and thus that bioclimatic SDMs may not alone constitute appropriate management tools for some non-native organisms. My dissertation demonstrates how the innovative application of molecular genetic techniques to the study of non-native populations can facilitate better understanding and management of potentially harmful biological invasions.




Previously Published In

Chapter 2 was originally published in Biological Invasions ( and is reprinted here with the permission of Springer Nature under License Number 5121390684485. Chapter 3 was originally published Open Access in Ecology and Evolution ( and is reprinted here under a CC-BY license.

Fieldsend, T.W., Dubos, N., Krysko, K.L., Raxworthy, C.J., and Malone, S.L. (2021) In situ adaptation and ecological release facilitate the occupied niche expansion of a non-native Madagascan day gecko in Florida. Ecology and Evolution, 11(14), 9410-9422.

Fieldsend, T.W., Krysko, K.L., Sharp, P., and Collins, T.M. (2021) Provenance and genetic diversity of the non-native geckos Phelsuma grandis Gray 1870 and Gekko gecko (Linnaeus 1758) in southern Florida, USA. Biological Invasions, 23(5), 1649-1662.



Rights Statement

Rights Statement

In Copyright. URI:
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).